Heat spreader for 4 x MRF151 VHF PA

These surplus high power PAs using 4 x MRF151 were originally used in watercooled industrial VHF drivers. The devices and some of the other components protrude about 2mm below the PCB lower surface.

To minimise the amount of copper required, I decided to make a heatspreader to go under the devices and make aluminium spacers for the rest. I also decided to make a fixture to hold the spreaders so I could cut neat pockets for the devices. Not sure that was a sensible approach. It certainly meant I had to do some tricky machining.

I have some more to make, I won’t be doing the fancy pockets this time, just transverse slots.

One of the completed PAs
Underside of the PA board
My over-complex pocketed heatrspreader
Underside of the spreader
Spreader bolted and slathered with Arctic Silver
Spreader and spacers showing the PCB-facing side
Output side aluminium spacer
input side spacer with driver device pocket
Assembled and ready to attach to the heatsink
I milled the giant heatsink flat and drilled and tapped some mounting holes
Two more of the finished items

Dish arm extension

Tony’s 1.2m dish has a figure-8 style extrusion for the feed arm, so clamps need to have two holes and a centre relief. For the new dual-band horn mount, we needed a bit more length, so I made up some extension plugs from aluminium

The plugs, turned from ally rod
The plugs pressed into place and fixed cap bolts on the underside
Clamp and mounting place with 10GHz WR90-fed WA6KBL and Super-VE4MA 5.7GHz feedhorns that I made for him

Coax clamp for 5.7GHz masthead unit

I wanted to avoid an extra plug/socket on the LDF1-50 coax feed from the 5.7GHz horn to the masthead transverter/PA, so I used a plastic cable gland, but there was still too much movement. This clamp bolts to the inside of the steel masthead box and holds the coax rigidly so I can plug directly into the coax relay without any danger of movement and fracture.